Tooth form mills in the form of end mills are used on gear cutting machines for gear cutting toothed wheels and for milling worm gears in accordance with the forming method. The use of such end mills starts with toothed wheels at, for instance, module 10 and extends up to the largest gear cutting dimensions. When milling worm gears, these end mills are also used with a much smaller module for worm gears and worm wheels.
Tools in end mill form or, even better, side milling cutters are also used for pre-milling for large gear cutting. End mills are preferably used where other tools are excluded, e.g., for collision reasons, such as in the manufacture of closed herringbone gears, of double helical gears with a small intermediate space or of workpieces in which no suitable runover path for a disk-shaped or worm-shaped tool exists; above all with gears with a large to very large module. In addition, a mill end tool is very inexpensive in comparison with a hob in this size range. The described method is thus also interesting for large gears with smaller batch sizes.
Suitable mounts are a requirement for the use of end mills in a gear cutting machine. The gear cutting machines are equipped for this purpose with a suitable end mill head which receives the end mill and drives it for rotation about a cutter axis. In known gear cutting machines, the cutter axis of the end mill extends perpendicular to the workpiece axis of the toothed wheel to be manufactured, whereby the manufacture of true herringbone gears and double helical gears with a small or no intermediate space is made possible with the aid of the end mill.
The end mills as a rule have a conical profile, with the profile diameter tapering in the direction of the end cutters. An example for a known end mill can be seen from the two FIGS. 1 and 2.
In particular FIG. 2 schematically shows the use of the end mill 1 for manufacturing an involute toothing at the toothed wheel 2. The end mill 1 is aligned with its longitudinal axis perpendicular to the workpiece axis and rotates about its cutter axis B for the one-sided/two-sided processing of the tooth flanks. The shape of the end mill is of a conical nature, with the diameter tapering in the direction of the end cutter 3. The diameter de of the end mill 1 in the region of the tooth head 4 is accordingly comparatively large with respect to the diameter d1 in the region of the tooth base 5.
The selected profile form of the end mill 1 effects a variable cutting speed vc over the total circumference of the cutter blade. The arrows 6 identify the resulting cutting speed profile along the cutter axis B, with the cutting speed vc2 of the highest amount being applied in the tooth head region and the minimal cutting speed vc1 being applied in the tooth base region. The selection of an ideal cutting speed for the rotational movement is not possible due to the diameter difference. On the one hand, a specific highest speed at the cutter tip may not be exceeded; on the other hand, a specific minimum cutting speed is required.
An irregular wear or blunting of the individual cutting regions along the cutter axis B occurs as a consequence of the speed profile 6 present. This makes a frequent sharpening of the end mill blades necessary to be able to ensure a sufficient machining quality. The possible cutter service life is furthermore disadvantageously impaired by it. The cutter service life can only be extended by setting lower average cutting speeds while taking account of the blade parts with a large diameter. To avoid a partial overload of the cutter, the cutter speed accordingly has to be adapted, which can result in longer machining parts overall.
It is the object of the present disclosure to overcome the above-disclosed disadvantages in form cutting using end mills.
This object is achieved by a gear cutting machine for cutting gears into a workpiece, in particular a toothed wheel. The gear cutting machine accordingly includes at least one cutter head for receiving at least one end mill. In accordance with the present disclosure, the cutter head or the end mill and/or the workpiece mount are made adjustable, whereby the end mill axis can be aligned approximately parallel to the machined tooth flank of the clamped workpiece. The cutter axis can be placed at the flank contour, with the end mill having an outer contour corresponding to the flank contour in accordance with the present disclosure.
A largely constant cutting speed over the total tooth flank of the workpiece to be prepared can hereby be achieved. The selection of a suitable rotational speed of the end mill about its cutter axis is moreover substantially simplified by the gear cutting machine in accordance with the present disclosure since an operation of the cutter in the ideal cutting speed range is possible over the total cutting surface and individual part regions do not have to be taken into account separately. Furthermore, regular wear occurs along the total cutting surface from the tooth head up to the tooth base, which has a positive effect on the achievable cutter service lives. Viewed overall, the machining time for the workpiece can also be optimized by this approach.
The end mill can advantageously be suitable for the manufacture of toothing profiles having cyclic curves such as involute toothing or cycloid toothing and/or as Wildhaber-Novikov gears as well as, optionally profiles composed thereof. Due to the required parallelism of the cutter axis and of the cyclic curve or involute of the workpiece to be manufactured, a cross-sectional profile of the end mill is accordingly necessary having comparatively slight diameter differences along the cutter axis. As a result, an approximately constant cutting speed profile can be achieved over the total tooth flank in the manufacture of these toothing arrangements.
The gear cutting machine in accordance with the present disclosure may be designed for a one-sided tooth flank machining. The cutter axis of the end mill can in each case be set approximately parallel to the tooth flank to be machined. The alignment of the end mill takes place either by adjusting the end mill or alternatively by moving the workpiece or the machining head tangentially to the toothing arrangement. A combined adjustment possibility of the end mill, of the machining head and of the workpiece is likewise possible in one example.
Possible embodiments of the end mill are also, in addition to complete cutters made from one piece (shaft tools), assembled cutters such as disposable cutting insert cutters or cutters having exchangeable heads.
The present disclosure is furthermore directed to an end mill for the form cutting of a workpiece toothing arrangement, in particular a gear toothing or similar profiles. In accordance with the present disclosure, the end mill has an almost unchanging diameter profile in the cutter axis direction, whereby an alignment of the cutter axis approximately parallel to the tooth flank to the machined or to the corresponding tooth flank section can be ensured for workpiece machining. The specific embodiment of the cutter blade depends on the flank shape to be manufactured. For example, slight fluctuations in the diameter profile are possible in end mills for involute toothing or cycloid toothing or arc toothing. In contrast to known conical end mills, they are, however, comparatively small. Only in this way can an almost constant cutting speed profile along the cutter axis be achieved. The embodiment of the end mill in accordance with the present disclosure is equally suitable for the milling of special toothing arrangements such as assembled profiles or asymmetrical toothed arrangements. Such profiles are disclosed, for example in WO 2005/060650, to whose content reference should be made at this passage of the description.
The end mill in accordance with the present disclosure is in particular suitable for use in a gear cutting machine in accordance with one of the above-explained advantageous embodiments. The end mill accordingly has the same advantages and properties such as have already been named in the description of the gear cutting machine in accordance with the present disclosure. A repeat explanation is therefore dispensed with at this point.
The present disclosure furthermore relates to a method of form milling a workpiece toothing arrangement, in particular a gear toothing arrangement, which is carried out on a gear cutting machine using an end mill. The inventive step in the claimed method is that the mill axis is aligned approximately parallel to the machined tooth flank to achieve an approximately constant cutting speed over the total cutter width.
The procedure in accordance with the present disclosure reduces the wear phenomena at the end mill used or keeps it constant over the total blade length. The method furthermore allows a simplified selection of an ideal cutting speed for operating the end mill since the diameter differences no longer differ so much along the cutter axis. Higher cutting speed can thus be used without there being a risk of a partial overload of certain cutter regions. This results in shorter workpiece machining times.
The method in accordance with the present disclosure in particular pursues a one-sided tooth flank machining of the workpiece to be manufactured or of a part region of the workpiece tooth flank. Accordingly, the end mill is aligned again after each machined tooth flank to ensure a parallel alignment of the cutter axis for the subsequent tooth flank.
The method in accordance with the present disclosure can advantageously be carried out on a gear cutting machine. An end mill can in particular be used for this purpose.
Further advantages and details of the present disclosure will be explained in more detail with reference to an embodiment and to corresponding drawings.